Our goal is to study how infection with Mycobacterium tuberculosis (MTB) regulates antigen (Ag) presenting cells (APCs, e.g.macrophages and dendritic cells). MTB is an important human pathogen that evades host defenses to maintain chronic infection. Dendritic cells must present MTB Ags to prime CD4 T cell responses, and CD4 effector T cells must recognize infected macrophages presenting MTB Ags to provide effector functions, including production of IFN-g, which is essential to host resistance. Regulation of macrophage ARC function by MTB is important to tuberculosis pathogenesis but remains poorly understood. We propose that Toll-like receptor (TLR) signaling by MTB pathogen-associated molecular patterns (PAMPs) produces both immune- activating effects (e.g.induction of pro-inflammatory cytokines by macrophages or maturation of dendritic cells) and late phase downregulatory effects (e.g.inhibition of MHC-II expression and Ag processing by macrophages that are chronically infected with MTB). We will investigate the ability of MTB PAMPs to signal via TLRs to modulate dendritic cell and macrophage APC function. We will focus on three major lipoprotein PAMPs of MTB that were identified in our previous studies, namely LpqH (19-kDa lipoprotein), LprG and LprA. We will study the ability of LpqH, LprG and LprA to signal via TLR2, TLR2/1 or TLR2/6, induce macrophage expression of pro-inflammatory cytokines, act as adjuvants to influence Th1/Th2 differentiation of T cell responses, promote dendritic cell maturation and cause late phase downregulation of macrophage MHC-II expression and Ag processing (including signaling and chromatin remodeling studies). Approaches will include production of recombinant His-tagged PAMPs and engineered variants for structure-function studies, generation of PAMP knockout MTB and M. bovis BCG and investigation of APC regulation by RFP-tagged mycobacteria in vivo with a mouse model of tuberculosis. Overall, these studies will enhance our understanding of tuberculosis pathogenesis and contribute to optimization of vaccine strategies for tuberculosis.